Rinsing Fluid for Lithography

ABSTRACT

The invention provides a novel rinsing fluid which can convert an easily wettable resist pattern surface having a contact angle of 40° or below into one having a contact angle of 70° or above to inhibit pattern collapse effectively and thereby give high-quality products. The rinsing fluid consists of a solution containing at least one fluorine compound soluble in water or alcoholic solvents which is selected from among compounds represented by the general formula (I),  
                 
 
those represented by the general formula (II),  
                 
 
and those represented by the general formula: R f ′—COOH: wherein R 1  and R 2  are each optionally substituted C 1-5  alkyl whose hydrogen atoms are partially or wholly replaced by fluorine, or R 1  and R 2  together with the SO 2  groups to which they are bonded and the nitrogen atom may form a five- or six-membered ring; R f  is optionally substituted C 1-5  alkyl whose hydrogen atoms are partially or wholly replaced by fluorine; m and n are each an integer of 2 or 3; and R f ′ is at least partially fluorinated alkyl having 8 to 20 carbon atoms.

TECHNICAL FIELD

The present invention relates to a rinse solution for lithographycapable of effectively preventing pattern falling during formation of afine pattern having a high aspect ratio.

BACKGROUND TECHNOLOGY

Along with the trend in recent years in the semiconductor devices towardcompact size and high integration, development works were practiced forthe use of light sources for the fine working including ultravioletlights such as the g-line and i-line, excimer laser beams such as KrFand ArF and the like as well as photoresist compositions suitablethereto such as, for example, chemical-amplification photoresistcompositions while many of the problems on the lithographic technologyin this direction are now on the way of solution.

Meanwhile, one of the problems is pattern falling during formation of afine resist pattern or, in particular, pattern of a high aspect ratio bythe lithographic technology. This pattern falling is a phenomenonencountered in the parallel formation of a large number of patterns on asubstrate that adjacent patterns are brought near as if leaning eachother eventually leading to breaking or exfoliation of the pattern atthe base part. If such pattern falling occurs, desirable products can nolonger be obtained resulting in a decrease of the product yield andreliability of the products.

Meanwhile, the reason for this pattern falling has already beenelucidated [Japanese Journal of Applied Physics, vol. 32 (1993), p.6059-p. 6064] and is understood to be caused by the surface tension ofthe rinse solution acting in the course of drying of the rinse solutionduring the rinse treatment of the resist pattern after development.

Accordingly, no forces to cause pattern falling are produced when theresist pattern is kept immersed in the rinse solution or, namely, duringthe rinse treatment after development but, in the course of the dryingstep to remove the rinse solution, forces due to the surface tension ofthe rinse solution act between the resist patterns leading to resistfalling.

Theoretically, therefore, pattern falling could be prevented by using arinse solution having a small surface tension or, namely, exhibiting alarge contact angle so that it was the attempt heretofore to preventpattern falling by the admixture of the rinse solution with an additivecompound capable of decreasing the surface tension or increasing thecontact angle.

For example, proposals were made for a rinse solution with addition ofisopropyl alcohol (JP6-163391A), a method in which the contact anglebetween the resist surface after development and the rinse solution isadjusted to be in the range of 60 to 120 degrees by using a mixture pfisopropyl alcohol and water or isopropyl alcohol and a fluorinatedethylene compound as the rinse solution (JP5-2993363A), a method ofusing a rinse solution having a surface tension adjusted in the range of30 to 50 dynes/cm by the addition of an alcohol, a ketone or acarboxylic acid for a resist by using a novolac resin or ahydroxypolystyrene resin as the base material of the resist composition(JP7-140674A), a method of adding a fluorine-containing surfactant to atleast one of the developer solution and the rinse solution(JP7-142349A), a method comprising a step of rinse with water and a stepof drying after replacement with a water-immiscible liquid having asmall surface tension and having a larger specific gravity than watersuch as, for example, a perfluoroalkyl polyether while the resist iskept immersed in water (JP7-226358A), a rinse agent compositioncontaining a nitrogen-containing compound having a molecular weight of45 to 10000 and having a hydrocarbon group with 1 to 20 carbon atoms andan amino group, imino group or an ammonium group in the molecule(JP11-295902A), a method of using a composition containing a fluorinatedcarboxylic acid, fluorinated sulfonic acid or a salt thereof as thedeveloper solution (JP2002-323773A), a method of treatment of thedeveloped substrate with an organic treatment agent containing ahydrofluoroether after a rinse treatment (JP2003-178943A andJP2003-178944A) and elsewhere.

With each of these rinse solutions or the rinse treatment methods,however, it is not possible to completely prevent pattern falling and,in addition, a risk of decrease is caused in the properties or, inparticular, the precision of the pattern formed thereby so that they arenot always satisfactory for industrialization.

On the other hand, the fluorine-containing surfactant used nowadays isperfluorooctane sulfonic acid (PFOS). This substance has a seriousproblem in handling because it is a “designated chemical substance”within Japan and also is an objective of the Significant novelutilization rules (SNUR) in the United States as an ecologicalinfluences-related rule. To say in particular, since the substancesunder the SNUR regulations may bring about an unreasonable risk todamage the health or environment necessitating wearing of protectors inthe working place and education and training of employees withinformation on the toxicity and so on with a further regulation on thediscarding treatment. It is accordingly desired to obtain afluorine-based surfactant capable of exhibiting equivalent effects as inthe use of the perfluorooctane sulfonic acid and containing afluorine-based surfactant with good handleableness and withoutenvironmental problems to replace the perfluorooctane sulfonic acid.

DISCLOSURE OF THE INVENTION

The present invention has been completed with an object to provide anovel rinse solution capable of effectively preventing pattern fallingby modifying the surface of a resist pattern highly wettable with acontact angle of 40 degrees or smaller so as to have a contact angle of70 degrees or larger to be suitable for production of high-qualityproducts.

The inventors have continued extensive investigations in order todevelop a rinse solution capable of effectively preventing patternfalling in the course of photoresist pattern formation by thelithographic technology still without causing a decrease in theproperties of the resist pattern after the treatment resulting infinding of the fact that, when the treatment is undertaken either beforeor after the rinse treatment with water by using a fluorinecompound-containing solution having a specific functional group, thecontact angle against the contacting liquid on the resist patternsurface can be increased to 70 degrees or larger without decreasing theproperties of the resist per se to prevent pattern falling leading tocompletion of the present invention on the base of this discovery.

Namely, the present invention provides a rinse solution for lithographycomprising a solution containing at least one kind selected from thefluorine compounds soluble in water or in an alcoholic solvent asrepresented by the general formula

(R¹ and R² in the formula are each an alkyl group or a substituted alkylgroup having 1-5 carbon atoms of which a part or all of the hydrogenatoms are substituted by fluorine atoms, R¹ and R² optionally forming afive-membered ring or six-membered ring jointly with the SO₂ and N towhich both are bonded), the general formula

(R_(f) in the formula is an alkyl group or a substituted alkyl grouphaving 1-5 carbon atoms substituted by fluorine atoms for a part or allof the hydrogen atoms and m and n are each an integer of 2 or 3)or the general formulaR_(f)′—COOH  (III)(R_(f)′ in the formula is an at least partly fluorinated alkyl grouphaving 8-20 carbon atoms).

The R¹ and R² in the general formula (I) preferably include alkyl groupsor substituted alkyl groups of which all of the hydrogen atoms aresubstituted by fluorine atoms such as, for example, perfluoroalkylgroups including perfluoromethyl group, perfluoroethyl group,perfluoropropyl group and perfluorobutyl group. Particularly preferableare those in which R¹ and R² jointly as bonded form a five-membered ringor six-membered ring together with the SO₂ group and the N atom to whichthey are bonded and all of the hydrogen atoms in the R¹ and R² aresubstituted with fluorine atoms such as, for example, a compoundexpressed by

The R_(f) in the general formula (II) is an at least partly fluorinatedalkyl group or substituted alkyl group having 1-5 carbon atoms. Thesubstituent group in this substituted alkyl group is exemplified byhydroxyl group, alkoxy group, carboxyl group and amino group. Aparticularly preferable R_(f) is a totally fluorinated one.

Such a compound is exemplified, for example, byperfluoro(3-morpholinopropionic acid),perfluoro(2-methyl-3-morpholinopropionic acid), perfluoro(4-morpholinobutyric acid) and the like, of which particularly preferable isperfluoro(2-methyl-3-morpholinopropionic acid) expressed by the formula

These fluorine compounds can be prepared by fluorinating a startingunfluorinated compound in a known method such as, for example, theelectrolytic fluorination method. Besides, lithium salts of those of thegeneral formula (I) in which the R¹ and R² are each a trifluoromethylgroup or a pentafluoroethyl group are commercially available under aregistered tradename of “Fluorad”.

Further, the fluorine compound represented by the general formula (III)can be exemplified by decane carboxylic acid, dodecane carboxylic acid,tetradecane carboxylic acid and hexadecane carboxylic acid substitutedby fluorine atoms for a part or all of the hydrogen atoms, of whichparticularly preferable are those of which all of the hydrogen atoms aresubstituted by fluorine atoms such as, for example, perfluoro(decanecarboxylic acid).

These fluorine compounds are used usually in the form of a solution asdissolved in water or in a mixture of water and an alcoholic solventsuch as, for example, methyl alcohol or ethyl alcohol.

Since fluorine compounds of a higher fatty acid are insoluble in water,it is necessary to use a mixed solvent of, for example, water and analcoholic solvent such as methyl alcohol, isopropyl alcohol andtrifluoroethanol. The mixing proportion of water and the alcoholicsolvent is in the range from 60:40 to 99:1 by the volume ratio.

Thus, the rinse solution of the present invention is prepared bydissolving the fluorine compound of the general formulas (I) to (III) inwater or in a mixed solvent of water and an alcoholic solvent in aconcentration of 0.001 to 5.0% by mass or, preferably, 0.01 to 1.0% bymass.

The treatment of the resist pattern with this rinse solution isconducted by dipping the resist pattern still wet after the developmenttreatment in the rinse solution or by coating or spraying the surface ofthe resist pattern with the rinse solution. By this treatment, thecontact angle of the resist pattern surface against the solution, whichmay occasionally be so small as to be 40 degrees or smaller, can beincreased so large as to be 70 degrees or larger or eventually 90degrees or larger so that drying can be effected without pattern fallingby conducting a drying treatment under this condition by means of spindrying and the like.

In the course of the treatment of the resist pattern with this rinsesolution, it is optional according to desire to increase the temperatureof the rinse solution. Since the surface tension of water, which is 72dynes/cm at 24° C., can be decreased to 62.6 dynes/cm at 80° C., patternfalling can further be decreased by increasing the temperature.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, best modes are described by way of examples forpracticing the present invention although the present invention is neverlimited by these examples.

An antireflection film having a film thickness of 77 nm was formed on asilicon wafer by coating with an antireflection filming agent (producedby Brewer Science Inc., product name ARC 29A) followed by a heatingtreatment at 215° C. for 60 seconds. This antireflection film was coatedwith a chemical-amplification positive-working photoresist prepared bydissolving a resinous ingredient expressed by the formula

and, relative to the resinous ingredient, 3.0% by mass oftriphenylsulfonium perfluorobutane sulfonate and 0.35% by mass oftriethanolamine in a mixed solvent of propyleneglycol monomethyletheracetate and propyleneglycol monomethyl ether (mixing proportion=6:4) togive an overall solid concentration of 11% by mass to form a photoresistfilm of 460 nm film thickness.

Onto the substrate having the thus formed photoresist film, alight-exposure treatment was conducted with a light of 193 nm wavelengthby using an ArF excimer stepper (a product by Nikon Corp., product nameNSR-S302A) followed by a heating treatment at 130° C. for 90 seconds.

Thereafter, a development treatment was conducted at 23° C. taking 60seconds by using a 2.38% aqueous solution of tetramethylammoniumhydroxide.

In the next place, the thus obtained line-and-space (110 nm/150 nm)pattern was treated with a 0.1% aqueous solution of a water-solubleresin obtained by copolymerizing an equal-amounts mixture of vinylpyrrolidone and vinyl imidazole to form a resist pattern having asurface with a contact angle of 25 degrees to water.

EXAMPLES 1-3

The resist patterns obtained in the Reference Example were subjected toa rinse treatment by using 3 kinds of rinse solutions including 0.005%aqueous solutions of perfluoro(2-methyl-3-morpholino propionic acid (aproduct by Jemco Inc., product name PFMO3, referred to hereinbelow asPFMO3), bis(heptafluoropropylsulfonyl)amine (a product by Jemco Inc.,product name EF-N331, referred to hereinbelow as EF-N331) andperfluoro(decane carboxylic acid) obtained on the market (referred tohereinbelow as PDC).

A mixed solvent of water and trifluoroethanol (volume proportion 99:1)was used as the solvent for PDC since this was insoluble in water.

This rinse treatment was conducted by dripping the aforementioned rinsesolutions for 3 seconds at 500 rotations followed by rinse for 20seconds with pure water.

The contact angles of the resist pattern surface before and after eachrinse solution treatment were determined by using a contact angle tester(a product by Kyowa Interface Science Co., product name CA-X150). Theresults are shown in Table 1. TABLE 1 Fluorine compound in Contactangle, degrees Example rinse solution Before treatment After treatment 1PFMO3 25 103 2 EF-N331 25 95 3 PDC 25 105

Further, the respective substrates after the treatment were examinedwith an SEM (scanning electron microscope) to find that absolutely nopattern falling and the like could be noted on the substrate surfaces.

COMPARATIVE EXAMPLE

Rinse treatments were undertaken in just the same manner as in Example 1by using pure water or isopropyl alcohol as the rinse solution to noteabsolutely no increase in the contact angle which remained at 25degrees. Further, the substrates after the treatment were examined withan SEM (scanning electron microscope) to detect resist pattern fallingoccurring in a considerable probability.

INDUSTRIAL UTILIZABILITY

By using the rinse solution of the present invention, it is possible toform a pattern without any pattern falling and still without anydecrease in the characteristics of the pattern properties even in thecases where the resist pattern to be formed is very fine as aline-and-space resist pattern of 30 to 100 nm and, in particular, havinga high aspect ratio of 3 or larger to be highly liable to patternfalling. Accordingly, the present invention can be satisfactory in themanufacture of semiconductor devices such as LSIs, ULSIs and the likeutilizing the lithographic method or, in particular, in the manufactureof devices having a high aspect ratio.

1. A rinse solution for lithography which is a solution containing atleast one kind selected from the fluorine compounds having solubility inwater or in an alcoholic solvent as represented by the general formula

(R¹ and R² in the formula are each an alkyl group or a substituted alkylgroup having 1-5 carbon atoms, of which a part or all of the hydrogenatoms are substituted by fluorine atoms, R¹ and R² optionally forming afive-membered ring or six-membered ring as bonded each to the othertogether with the SO₂ or N to which the same are bonded), the generalformula

(R_(f) in the formula is an alkyl group or a substituted alkyl grouphaving 1-5 carbon atoms, of which a part or all of the hydrogen atomsare substituted by fluorine atoms, and m and n are each an integer of 2or 3), or the general formulaR_(f)′—COOH (R_(f)′ in the formula is an at least partly fluorinatedalkyl group having 8-20 carbon atoms).
 2. The rinse solution forlithography described in claim 1 wherein the fluorine compound havingsolubility in water or in an alcoholic solvent is a compound expressedby the formula


3. The rinse solution for lithography described in claim 1 wherein thefluorine compound having solubility in water or in an alcoholic solventis a compound expressed by the formula


4. The rinse solution for lithography described in claim 1 wherein thefluorine compound having solubility in an alcoholic solvent is acompound expressed by the formulaC₁₀F₂₁COOH.
 5. The rinse solution for lithography described in claim 1which is a solution with water used as the solvent.
 6. The rinsesolution for lithography described in claim 1 which is a solution with asolvent mixture of water and an alcoholic solvent used as the solvent.7. The rinse solution for lithography described in claim 1 which is usedfor treatment of a resist pattern having a surface with a contact angleof 40 degrees or smaller.